1. Field of the Present Invention
The present invention relates to a spindle motor centering device, and more particularly, to a centering device installed on a thin-type spindle motor to carry out the centering of a disk with respect to the rotating shaft of the spindle motor.
2. Description of the Related Art
The rising development of information storage media due to the progress in information technologies has caught a lot of attention. In this rising development, the spindle motor has been playing a key role. The spindle motor, being compact in size, has become the most popular device for driving an information storage media such as an optical disk drive or a floppy disk drive. There are various types of spindle motor, any one of which mainly includes a rotating shaft, a rotor, a stator, and a supporting surface for bearing and carrying an optical disk. Here, the supporting surface can be the surface of a separately provided supporting plate or the surface of the motor rotor itself.
Since the spindle motor usually drives the optical disk at a high rotating speed in the order of thousands of revolutions per minute (rpm), especially when applied to drive a DVD-ROM, the radial run-out accuracy of the optical disk is strictly required. Generally, an optical disk has a tolerance of at least 0.15 mm in the radius of its central hole, and the error in the radius of its central hole may significantly influence its radial run-out accuracy. In order to reduce or avoid the radial run-out of the optical disk caused by the error in the radius of its central hole, a centering device is usually installed on the spindle motor for holding and centering the optical disk so as to prevent the radial run-out of the optical disk and thus to improve the reading, playing, and recording accuracy of the optical disk.
FIGS. 1A and 1B, respectively, show the top view and the sectional view of a conventional spindle motor centering device. As illustrated in FIG. 1A and FIG. 1B, a spindle motor 1 includes a stator 5 around which is wound with coils 6, a shaft 2 supported within the stator 5 through a bearing 3 and a washer 4, a rotor 7 on which is installed with a permanent magnet 8, an anti-slip sheet 9 for preventing an optical disk (not shown) mounted thereon from sliding, and a centering device 10, made of resin, for holding and centering the optical disk. The centering device 10 includes a body portion 10b provided with a central hole for accommodating the shaft 2 of the spindle motor, and several centering elastic fingers 10a each of which has a free end extending from the body portion 10b in the axial direction of the spindle motor 1 as shown in FIGS. 1B and 2. When an optical disk 13 is mounted onto a predetermined axial position in the spindle motor 1 as shown in FIG. 2, some centering elastic fingers 10a contact and urge against the surface of the central hole of the optical disk 13 so as to center the optical disk 13.
In another conventional spindle motor centering device as shown in FIGS. 3A and 3B, a separate supporting plate 14 is additionally provided on the surface of the rotor 7 to bear and carry the optical disk. Similar centering device includes a body portion 16, and several centering elastic fingers 15 extending from the body portion 16 are used to process the centering of the optical disk.
However, as the spindle motor continuously becomes thinner, the free end of the conventional centering elastic finger, extending in the axial direction of the spindle motor, are shortened gradually which, in turn, causes the rigidity of the centering elastic finger to become larger and larger. The increased rigidity of the centering elastic finger further causes an increased resistance, generated by the centering elastic fingers, tending to hinder the optical disk from being moved to its predetermined axial position, and thus makes the mounting of the optical disk difficult. Besides, the conventional centering device further suffers from the problem of resin fatigue in the centering elastic fingers caused by repeated bending due to repeated contacts between the centering elastic fingers and the optical disk, and also from the problem of creep due to operation under high temperature.